Daimler recalls newly launched Mercedes-Benz eCitaro electric buses, equipped with optional solid-state batteries (SSB), due to the potential of short circuits in the cell modules.
According to Electrive, operators that recently received the eCitaros with SSB were notified in February about the issue and put a total of about 30 vehicles out of service. The manufacturer has to check a possible insulation fault.
In the case of ESWE in Wiesbaden, Germany, 21 eCitaros with SSB arrived in early February, and were removed from service shortly thereafter. The operator was forced to use diesel vehicles for about two weeks already. MVG from Munich is less affected, with two vehicles.
According to the report, the problem is in the cell modules. The specific solid-state batteries are supplied by Bolloré's subsidiary Blue Solutions. Those are Lithium Metal Polymer (LMP) batteries (offered since 2012), which operate in temperatures between 50°C and 80°C.
"“As part of our ongoing product monitoring, we have determined that there may be an insulation defect in the cell modules of Mercedes-Benz eCitaro vehicles with solid high-voltage batteries. Due to the insulation fault, a cell short circuit can occur within the battery,” the commercial vehicle manufacturer tells electrive.net. The solid-state batteries come from the French company Blue Solutions..."
Mercedes-Benz offers two battery options for 18m articulated eCitaro G model:
- standard lithium-ion batteries (NCM, with liquid electrolyte)
296-396 kWh (9 to 12 packs, 33 kWh each)
real-world range of up to 170 km (106 miles)
- solid-state batteries - Bolloré's subsidiary Blue Solutions Lithium Metal Polymer (LMP)
up to 441 kWh (seven 63 kWh packs)
up to 190 km (118 miles) of range
The SSB has a higher energy density (at least compared to the specific NCM option), so the range can be slightly higher, but they are not set up for ultra-fast charging.
Moreover, their operating temperatures between 50°C and 80°C are quite high. The industry is still searching for solid-state batteries that would work in "normal" temperatures, like 20°C.
This is the major hurdle of the LMP cells, because in the car application, customer don't want to wait until the battery is warm (the buses can keep the battery temperature for 5-7 days in a week). On the other hand, there is no need for any cooling of the cells.
Blue Solutions has currently two LMP production lines (500 MWh/year each) - one in Quimper in Brittany, France, and the second one in Montreal in Quebec, Canada. The company is now in the process of installing a third line at its plant in Quimper to add another 500 MWh for a total of 1.5 GWh annually. According to Electrive, both plants are fully loaded with orders and work 24/7.
The energy density is "more than 250 Wh/kg" depending on the application so not a world record (it was one of the highest results when launched almost a decade ago though). An interesting advantage of the LMP is a guarantee of over 4.000 cycles of using the full capacity.